Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

lastKey()
last().getValue()
get(lastKey())
successors(k)
tailMap(k).entrySet().iterator()
predecessors(k)
headMap(k).entrySet().iterator()
9.5.3 Flight Databases and Maxima Sets
As we have mentioned in the preceding sections, unordered and ordered
dictionaries have many applications.
In this section, we explore some specific applications of ordered dictionaries.
Flight Databases
There are several web sites on the Internet that allow users to perform queries on
flight databases to find flights between various cities, typically with the intent to
buy a ticket. To make a query, a user specifies origin and destination cities, a
departure date, and a departure time. To support such queries, we can model the
flight database as a dictionary, where keys are Flight objects that contain fields
corresponding to these four parameters. That is, a key is a tuple
k = (origin, destination, date, time).
Additional information about a flight, such as the flight number, the number of
seats still available in first (F) and coach (Y) class, the flight duration, and the
fare, can be stored in the value object.
Finding a requested flight is not simply a matter of finding a key in the dictionary
matching the requested query, however. The main difficulty is that, although a
user typically wants to exactly match the origin and destination cities, as well as
the departure date, he or she will probably be content with any departure time that
is close to his or her requested departure time. We can handle such a query, of
course, by ordering our keys lexicographically. Thus, given a user query key k,
we can call successors(k) to return an iteration of all the flights between the
desired cities on the desired date, with departure times in strictly increasing order
from the requested departure time. A similar use of predecessors(k) would
give us flights with times before the requested time. Therefore, an efficient
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